Oral Presentation
Physical Properties of HII regions in Nearby Galaxies
Presenter: Hsi-An Pan (Tamkang University)
HII regions have long been used as the probes of massive star formation in galaxies. Since the Hα luminosity of an
HII region is related to the amount of ionizing radiation emitted by the OB stars, HII region provides fruitful information on the location of massive star formation, the rate of star formation, and the mdoe of star formation (e.g., single or clustered star formation).
We constructed HII region catalog for ~ 70 nearby galaxies using the narrowband-Hα imaging from the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) survey. The catalog contains various physical properties of HII regions, such as their location in a galaxy, Hα luminosity, size and orientation, and the associated galactic environment. To our knowledge, this is by far the largest HII region catalog with cloud-scale resolution. At the resolution (~100 pc) at which the individual star-forming regions can be identified, we find that the shape of HII region luminosity function varies from galaxy to galaxy, and also varies with galactic environments (bulge, stellar bar, and spiral arms, etc.), indicating the existence of a deep connection between galactic dynamics and star formation. Moreover, a similar dependence is also observed for the mass function of giant molecular clouds (GMCs), suggesting a tight correlation between the properties of new-born stars and their parent GMCs.
These initial results imply that environment may play a role in determining how stars form in galaxies. Quantification of the environmental dependence would provide clues into the star formation process. In the future, we will constrain star formation efficiency of GMCs and initial mass function by cross-comparison of mass/luminosity function of GMCs (from PHANGS-ALMA), HII regions (PHANGS-Hα) and star clusters (PHANGS-HST).
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